Oil shale retorting and combustion system

Abstract

The present invention is directed to the extraction of energy values from oil shale containing considerable concentrations of calcium carbonate in an efficient manner. The volatiles are separated from the oil shale in a retorting zone of a fluidized bed where the temperature and the concentration of oxygen are maintained at sufficiently low levels so that the volatiles are extracted from the oil shale with minimal combustion of the volatiles and with minimal calcination of the calcium carbonate. These gaseous volatiles and the calcium carbonate flow from the retorting zone into a freeboard combustion zone where the volatiles are burned in the presence of excess air. In this zone the calcination of the calcium carbonate occurs but at the expense of less BTU's than would be required by the calcination reaction in the event both the retorting and combustion steps took place simultaneously. The heat values in the products of combustion are satisfactorily recovered in a suitable heat exchange system.

What is claimed is: 
     
       1. A method for extracting energy values from oil shale having substantial concentrations of calcium carbonate therein, comprising the steps of heating particulate oil shale in a retorting zone in a bed reactor, fluidizing the contents in said zone with air having an oxygen content of about stoichiometric and sufficient to provide for the heating of oil shale to a temperature adequate to thermally decompose the organic hydrocarbons therein and insufficient to provide a temperature adequate to effect substantial combustion of the hydrocarbons extracted from the oil shale or substantial calcination of the calcium carbonate, conducting the extracted hydrocarbons and the calcium carbonate in an upward direction into a freeboard combustion zone, contacting the contents in said freeboard combustion zone with excess air having an oxygen level in the range of about 10 to 85 percent greater than stoichiometric to provide a temperature sufficient to effect the combustion of said volatiles and the calcination of said calcium carbonate in said combustion zone, thereafter extracting sensible heat from the resulting combustion products. 
     
     
       2. The method claimed in claim 1, including the additional step of conducting the flow of the products of combustion emanating from the combustion zone in a direction opposite to the upward direction of flow of the extracted hydrocarbons and calcium carbonate being conducted from the retorting zone into the combustion zone to provide a radiation arch for controlling nitrogen oxides emission and for reducing ash crown build up on horizontal surfaces in the flow path of the products of combustion.